[B2-devel] Video switching problem and VOSF/DA

[Gwenole B. <gb...@di...>]

Hi,

Some users have been reporting problems with B2 crashing right at startup.
I never could reproduce it until today. B2 is built with VOSF and direct
addressing enabled. The problem occurs when I remove my
~/.basilisk_ii_xpram. Then I simply launch B2 again and it crashes.

do_handle_screen_fault: unhandled address 0x42877460 [IP=0x80b45cb]
[...]
0202e8e8: 2815 28c4 c081 c284 8287 MOVE.L (A5),D4

Toying with video code, I noticed that this address was actually a
previously allocated screen buffer that is no longer valid because of a
mode switch.

Before the switch I had:

the_buffer = 0x42877000, the_buffer_copy = 0x4290e008, the_host_buffer =
0x427e0000, the_buffer_size = 618496
VideoMonitor.mac_frame_base = 021a7000

Then after:

the_buffer = 0x4290e000, the_buffer_copy = 0x820cb18, the_host_buffer =
0x8203470, the_buffer_size = 40960
VideoMonitor.mac_frame_base = 0223e000

1) Notice that MacOS 8 seems to be willing to switch to 1-bit mode

2) It's obvious that the previous screen buffer is gone

3) For some reason, though VideoMonitor.mac_frame_base contains the new
virtual (MacOS address space) frame buffer, MacOS is still using the old
screen buffer after the switch from VideoDriverControl(), hence the crash.

4) In slot_rom.cpp/InstallSlotROM(), VideoMonitor.mac_frame_base is used
only once at ROM patching time.

Solutions:

1) Should I patch Frame buffer base in SlotROM whenever we call
set_mac_frame_buffer() with new values?

2) Check whether VidLocal.desc updated when it ought to be?

Other ideas?

Thanks,
Gwenole.